In recent years, a processing technology for transferring a fine structure on a mold onto a member to be processed, such as a resin material, a metal material, or the like, has been developed and has received attention (Stephan Y. Chou, et al., Appl. Phys. Lett., Vol. 67, Issue 21, pages 3114-3116 (1995)). This technology is called nanoimprinting or nanoembossing, and provides a resolution on the order of several nanometers. For this reason, the technology has been increasingly expected to be applied to next-generation semiconductor manufacturing technologies in place of light exposure devices, such as a stepper, a scanner, and the like. Further, the technology is capable of collectively processing a three-dimensional structure at a wafer level, so that the technology has been expected to be applied to a wide variety of fields, such as manufacturing technologies for optical devices, such as photonic crystals and biochips, such as μ-Tas (Micro Total Analysis System).
In a case when such a processing technology is applied to the semiconductor manufacturing technology, the processing technology is performed in the following manner.
A work (workpiece), including a substrate (e.g., a semiconductor wafer) and a photocurable resin material layer disposed on the substrate, and a mold, on which a desired imprint (projection/recess) pattern, is formed, are disposed opposite to each other and between the work and the mold, and the resin material is filled, followed by irradiation of ultraviolet (UV) light to cure the resin material.
By this, the above pattern is transferred onto the resin material layer and then etching, or the like, is effected by using the resin material layer as a mask, so that pattern formation on the substrate is performed.
In a case when the (nano-) imprint method is used as lithography for the semiconductor manufacturing technology, a step-and-repeat method, in which a mold is prepared depending on a chip to be produced and a pattern on the mold is repeatedly transferred onto a substrate, is available. This is because it is possible to improve the accuracy by reducing an integral error of alignment and the mold pattern itself due to an increase in wafer size, and it is possible to reduce a production cost of the mold increased by the increase in the wafer size.
In the resin material layer transferred on the substrate, as an underlying portion of the pattern, a thick portion, which is generally called a residual film, is present. By removing the residual film, a mold layer for processing the substrate is completed. Herein, this mold layer is referred to as an “etching barrier”.
As a conventional imprint method, Japanese Laid-Open Patent Application No. 2000-194142 proposes a method (process), in which an etching barrier is formed by a single layer of a UV-curable resin material, and the entire surface of the layer is etched. Such a process is referred to herein as a “single layer process”). Further, such a process that a thickness is uniformly reduced by etching the entire surface is referred to herein as an “etch back” process.
U.S. Patent Application Publication No. 2006/0060557 proposes a method (process) for forming a reverse pattern by using a resin material layer and a material capable of ensuring an etching selection ratio with the resin material layer. In this method, a reverse layer of the material capable of ensuring an etching selection ratio with the resin material layer is applied onto the resin material layer, and then, an etch back process is performed until a projection of the resin material layer is exposed. Finally, the resin material layer is etched by using the reverse layer embedded in a recess of the resin material layer as a mask. Herein, such a process is referred to as a “reverse process”. In the reverse process, the resultant etching barrier has a more perpendicular processing shape, and the dimensional accuracy thereof is also enhanced.
In a case when a pattern is formed on a substrate by the above-described conventional imprint method, the following problem can arise.
That is, as shown in FIG. 8, when imprinting for one shot is performed, a resin material can be pressed out of a shot area to form an outside area (extrusion area) 1254 extending on a substrate 1253 along an edge of a mold 1251. The resin material layer in this outside area 1254 has a thickness more than that of the resin material layer in a processed area 1255, in many cases. For example, the thickness of the resin material layer or a height or a depth of projections or recesses of an imprint pattern in the processed area 1255 is several tens of nanometers to several hundreds of nanometers, whereas the thickness of the resin material layer in the outside area 1254 can be several micrometers.
In the case of using imprinting for semiconductor lithography, as described above, the step-and-repeat method is suitable. However, when the pattern transfer onto the substrate is repeatedly performed by the step-and-repeat method, the outside area 1254 is formed for each shot.
By the formation of such an outside area 1254, a problem can arise that an etching characteristic is different between that in the neighborhood of the outside area and that in an area apart from the outside area. For example, in the case when a projection structure on an order that is considerably larger than the imprinting pattern is present in the neighborhood, a distribution of an electrical field of plasma during etching can be disturbed, or flow of an etching gas can be prevented. Further, the etching includes a chemical reaction, so that in the neighborhood of the outside area where an exposed area of the resin material layer is very large, compared with the area apart from the outside area, consumption of an etching gas can be required locally in a large amount. As a result, such a phenomenon that the etching characteristic in the neighborhood of the outside area is different from that in the area apart from the outside area can occur.